A fuel cell system includes a coolant circuit through which coolant flows to cool a fuel cell. The coolant circuit includes an ion exchanger that removes metal ions from the coolant by adsorbing the metal ions on an ion exchange resin (refer to, for example, Japanese Laid-Open Patent Publication No. 2013-233499).
The ion exchanger of the above patent document includes a case. The case includes an intake port, which draws coolant into the case, and a discharge port, which discharges coolant out of the case. A lid is arranged on an upper open end of the case. A cartridge, which is fixed to the lid, accommodates an ion exchange resin. A cylinder, which is accommodated in the case, is formed integrally with the lower surface of the lid. The cartridge is fixed to the inner circumferential surface of the cylinder in a removable manner. The cylinder includes a communication hole through which the inner side of the cylinder is in communication with an upper one of the intake port and the discharge port.
In the ion exchanger of the above patent document, when coolant is drawn through the intake port and into the case, the ion exchange resin adsorbs metal ions from the coolant as the coolant flows through the cartridge. The coolant from which the ions have been removed is discharged out of the case through the communication hole and the upper port.
In the ion exchanger of the above patent document, the cartridge is fixed to the lid. Thus, the lid and the cartridge are removed from the case simultaneously. Accordingly, when exchanging the cartridge, the intake port and a connection port do not have to be removed from a pipe of the coolant circuit. This facilitates the exchanging of cartridges.
However, the ion exchanger of the above patent document has a shortcoming in which the cylinder includes a void above the communication hole. Thus, air, which enters the cylinder together with the coolant, is apt to remain in the void, that is, immediately below the lower surface of the lid. The residual air is suddenly discharged from the ion exchanger to a coolant pipe. As a result, a large amount of air will flow into a pump arranged in the coolant circuit. This may cause a discharge failure of the pump such as cavitation. Further, when a large amount of air flows into the fuel cell, the fuel cell is cooled unevenly.